Display element having filter material diffused in a substrate of the display element

ABSTRACT

Optical filter functionality is incorporated into a substrate of a display element thereby decreasing the need for a separate thin film filter and, accordingly, reducing a total thickness of a filtered display element. Filter functionality may be provided by any filter material, such as pigment materials, photoluminescent materials, and opaque material, for example. The filter material may be incorporated in the substrate at the time of creating the substrate or may be selectively diffused in the substrate through a process of masking the substrate, exposing the substrate to the filter material, and heating the substrate in order to diffuse the filter material in the substrate.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 60/613,481, filed on Sep. 27, 2004,which is hereby expressly incorporated by reference in its entirety.

FIELD OF THE INVENTION

The field of the invention relates to microelectromechanical systems(MEMS).

DESCRIPTION OF THE RELATED TECHNOLOGY

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF THE INVENTION

In one embodiment, a method of forming a display device comprises thesteps of diffusing a material into a substrate, said material having adifferent optical property than said substrate, and forming at least onelight modulating element over the substrate, the light modulatingelement comprising a partially reflective surface and a substantiallyreflective surface that form an optical cavity, at least one of saidreflective surfaces movable with respect to the other to modulate saidoptical cavity.

In another embodiment, a display device comprises at least one lightmodulating element comprising first and second reflective surfaces, saidsecond surface being movable with respect to said first surface, and asubstrate, said light modulating element disposed over said substrate,wherein said substrate comprises a color filter that transmits colorlight when illuminated by white light.

In another embodiment, a display device comprises at least onelight-modulating element comprising first and second reflectivesurfaces, said second surface being movable with respect to said firstsurface, and a substrate, said light-modulating element disposed oversaid substrate, wherein said substrate incorporates at least onepatterned mask.

In another embodiment, a display device comprises a plurality oflight-modulating elements each comprising first and second reflectivesurfaces, said second surface being movable with respect to said firstsurface, and a substrate, said plurality of light-modulating elementsdisposed over said substrate, wherein said substrate includes thereinfirst absorptive regions, said absorptive regions having differentoptical transmission properties than second regions in said substratedisposed between said first absorptive regions.

In another embodiment, a display device comprises at least one pluralityof light modulating elements each comprising first and second reflectivesurfaces, said second surfaces being movable with respect to said firstsurfaces, and a substrate, said at least one plurality of lightmodulating elements disposed over said substrate, wherein said substratecomprises a plurality of elements configured to limit a field-of-view ofthe display device.

In another embodiment, a method of forming an interferometric modulatorcomprises the steps of combining a substrate material with a filtermaterial in order to form a mixture, heating the mixture so that thesubstrate material substantially melts and the filter material isdiffused within the melted substrate material, cooling the mixture inorder to form a substrate, and forming at least one light modulatingelement over the substrate, the light modulating element comprising apartially reflective surface and a substantially reflective surface thatform an optical cavity, at least one of said reflective surfaces movablewith respect to the other to modulate said optical cavity.

In another embodiment, a method of operating a display device comprisesthe steps of illuminating an array of light modulating elements over asubstrate, the substrate incorporating a filter material diffusedtherein, the light modulating element comprising a partially reflectivesurface and a substantially reflective surface that form an opticalcavity, at least one of said reflective surfaces being movable withrespect to the other to modulate said optical cavity, and viewing lightreflected from the array of light modulating elements, wherein as anangle between a direction of the reflected light and a normal to thesurface of the substrate increases, a filtering performed by the filtermaterial increases.

In another embodiment, an apparatus comprises a display comprising oneor more light modulating elements. In one embodiment, each lightmodulating element comprises first and second reflective surfaces, saidsecond surface being movable with respect to said first surface, and asubstrate having a filter material diffused therein, said lightmodulating element being disposed over said substrate, a processor thatis in electrical communication with said one or more light modulatingelements, said processor being configured to process image data. In oneembodiment, the apparatus further comprises a memory device inelectrical communication with said processor.

In another embodiment, a display device comprises means for modulatinglight, and means for supporting said light modulating means, and meansfor filtering light disposed in said supporting means.

In another embodiment, a display device comprises means for modulatinglight, and means for supporting said light modulating means, and meansfor limiting a field-of-view.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 is a cross section of an interferometric modulator having darktinting in selected portions of the substrate.

FIG. 9 is a cross section of an interferometric modulator having coloredtinting in the substrate.

FIG. 10 is a cross section of an interferometric modulator havingselective colored tinting in the substrate, wherein multiple colors oftinting are selectively incorporated in the substrate.

FIG. 11A is a cross section of another interferometric modulator havingcolored tinting in the substrate.

FIG. 11B is a graphical diagram illustrating the spectral response ofone embodiment that includes a green modulating element and a substrateincorporating magenta filtering material.

FIGS. 12A illustrate an interferometric modulator having field-of-viewfilter incorporated in the substrate.

FIGS. 12B-12C illustrate an exemplary method of fabricatingfield-of-view filters in a substrate.

FIG. 13 is a cross section of an interferometric modulator havingphotoluminescent materials in the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description is directed to certain specificembodiments of the invention. Various embodiments of the invention, forexample, relate to incorporating optical filter functionality into asubstrate of a display element. Filter functionality may be provided byany filter material, such as pigment materials, fluorescent materials,and opaque material, for example. The filter material may beincorporated in the substrate at the time of creating the substrate ormay be selectively diffused in the substrate through a process ofmasking the substrate, exposing the substrate to the filter material,and heating the substrate in order to diffuse the filter material in thesubstrate.

The invention, however, can be embodied in a multitude of differentways. In this description, reference is made to the drawings whereinlike parts are designated with like numerals throughout. As will beapparent from the following description, the embodiments may beimplemented in any device that is configured to display an image,whether in motion (e.g., video) or stationary (e.g., still image), andwhether textual or pictorial. More particularly, it is contemplated thatthe embodiments may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,wireless devices, personal data assistants (PDAs), hand-held or portablecomputers, GPS receivers/navigators, cameras, MP3 players, camcorders,game consoles, wrist watches, clocks, calculators, television monitors,flat panel displays, computer monitors, auto displays (e.g., odometerdisplay, etc.), cockpit controls and/or displays, display of cameraviews (e.g., display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures, packaging, and aesthetic structures (e.g., display of imageson a piece of jewelry). MEMS devices of similar structure to thosedescribed herein can also be used in non-display applications such as inelectronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. In some embodiments, the layers are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a panel or display array (display) 30. The cross section ofthe array illustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. ForMEMS interferometric modulators, the row/column actuation protocol maytake advantage of a hysteresis property of these devices illustrated inFIG. 3. It may require, for example, a 10 volt potential difference tocause a movable layer to deform from the relaxed state to the actuatedstate. However, when the voltage is reduced from that value, the movablelayer maintains its state as the voltage drops back below 10 volts. Inthe exemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, it will be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to the processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to the arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields some portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34 and the busstructure 44. This allows the shielded areas to be configured andoperated upon without negatively affecting the image quality. Thisseparable modulator architecture allows the structural design andmaterials used for the electromechanical aspects and the optical aspectsof the modulator to be selected and to function independently of eachother. Moreover, the embodiments shown in FIGS. 7C-7E have additionalbenefits deriving from the decoupling of the optical properties of thereflective layer 14 from its mechanical properties, which are carriedout by the deformable layer 34. This allows the structural design andmaterials used for the reflective layer 14 to be optimized with respectto the optical properties, and the structural design and materials usedfor the deformable layer 34 to be optimized with respect to desiredmechanical properties.

It can sometimes be advantageous to place various types of filtersbetween the viewer and the interferometric modulator structures toenhance the quality of the display. In some cases, these filters may beseparate from the interferometric modulator structure and placed betweenthe substrate and the viewer. Such separate filters have the advantageof easy replacement, however, overall thickness of the interferometricmodulator display package is increased and in some cases additionaloptical complications can arise due to the filter-air-substrateinterfaces. In other cases, the filter may be incorporated into a filmthat is formed on or adhered to one or more surfaces of the substrate.However, it may be difficult to incorporate the desired filterfunctionality into the film due to its thinness.

In various embodiments of the present invention, filter functionality isincorporated into the substrate of the interferometric modulator itself,eliminating the need for a separate structure. Such a system maysimplify manufacturing of interferometric modulators and reduce athickness of interferometric modulators that include filters. Inaddition, inclusion of filters in a substrate, rather than in a separatethin film, for example, may decrease the interferometric modulator'ssensitivity to moisture and resistance to scratching. Specificnon-limiting examples of substrate filter systems are described below.

FIG. 8 is a cross sectional side view of an interferometric modulator800 having dark tinting in selected portions of the substrate. Theinterferometric modulator 800 comprises a movable mirror 806 separatedfrom a partial reflector 802 by supports 804. In FIG. 8, the partialreflector 802 is adjacent a substrate 810 that includes selective darktinting 830. Exemplary FIG. 8 also illustrates a dielectric 820 in theinterferometric modulator and a viewing eye 510. As used herein, theterm “light modulating element” and “modulating element” are usedinterchangeably and each include the structures between, and including,a movable mirror and a partial reflector of the interferometricmodulator. With reference to FIG. 8, for example, a light modulatingelement 860 comprises the structure between, and including, the movablemirror 806 and the partial reflector 802.

As illustrated in FIG. 7A, for example, portions of support structures18 are visible to a viewer through the substrate 20. These supportstructures 18 may have inherent reflectivities that may decrease thecontrast and sharpness of the interferometric modulator based images.Furthermore, edge portions 807 (FIG. 8) of each interferometricmodulator 800 (FIG. 8) may exhibit reflectivity even when theinterferometric modulator is driven to a dark state because the movablemirror 806 at the edge portions 807 will not fully collapse. Therefore,it may be advantageous to use patterned dark filtering to mask thereflectivity of support structures and edge portions of interferometricmodulators while still permitting unobstructed viewing of the center ofeach interferometric modulator structure.

Accordingly, the substrate 810 may include regions 830 with dark tinting830 separated by regions without such dark tinting. The dark tinting canrange from lightly tinted to substantially dark tinted. In some cases,the tinting may be colored. The range of tint of the color and also varyfrom light coloring to deep coloration. A stripped, checkered, orcrisscross pattern may be used. Other patterns are also possible.

In one embodiment, a patterned dark tinting 830 is incorporated into thesubstrate 810 using pigments. Any absorber pigments known in the art fordark tinting (e.g., of glass or polymer) may be incorporated into thesubstrate 810. Other types of pigments or dyes or other material, bothwell known, or yet to be devised may be employed.

In one embodiment, the material 830 is formed in the substrate 810 byforming patterns of filter material, such as a pigment material, on thesurface of the substrate, followed by softening of the glass to allowthe filter material to diffuse into the interior of the substrate 810.More particularly, exemplary processes of incorporating dark tinting830, or any other filters described herein, in the substrate 810 mayinvolve masking portions of the substrate, applying the filter materialto the substrate, and diffusing the filter material in the substrate.These processes may be accomplished in several manners, a few of whichare described below.

In one embodiment, a shadow mask comprising a thin sheet of metal, orother rigid material, is patterned with holes that correspond withportions of the substrate into which the filter material is to bediffused. The shadow mask may then be placed on the substrate and thefilter material applied to the substrate. After applying the filtermaterial, the shadow mask may be removed, leaving the filter materialonly on the desired areas.

In another embodiment, the filter material may be applied directly tothe substrate using an ink-jet printing technique, for example, In thisembodiment, the filter material may be applied only on those portions ofthe substrate that are to diffuse the filter material. In anotherembodiment, ink-jet printing techniques may be used to form a mask onthe substrate, wherein the mask corresponds with non-filtered portionsof the substrate, such as portions of the substrate 810 between darktinting 830 in FIG. 8.

In certain embodiments, filter material is applied to the substrate 810using an adhesive medium, such as alcohol, for example, that is bound tothe filter material. In an advantageous embodiment, the adhesivematerial is evaporative so that when the substrate 810 is later heated,the adhesive material will be removed from the substrate 810. In anotherembodiment, the filter material does not include an adhesive material,but is held in place on the substrate 810, for example, by gravity.Other methods may also be used to expose the unmasked portions of thesubstrate 810 to the filter material.

In another embodiment, the filter material is applied to selectedportions of the substrate using photolithography techniques. In oneembodiment, the filter material is first applied to the entiresubstrate. A photoresist material is then coated on the filter materialand is patterned using an appropriate light source. The patternedportions of the photoresist material may then be removed using asolvent, leaving the photoresist material only on those portions thatare to have the filter material diffused in the substrate. In oneembodiment, the same solvent, or an additional solvent, removes thefilter material from the patterned portions so that when the remainingphotoresist material is removed, the filter material remains only on thedesired areas of the substrate.

With the filter material on the substrate, using any one or more of thetechniques described above or other suitable techniques, the substrate810 is heated to a temperature sufficient to diffuse the filter materialinto the substrate 810. In one embodiment, the substrate 810 is heatedto a temperature in the range of about 200-250 degrees Celsius. Inanother embodiment, the substrate 810 is heated to a temperature in therange of about 150-300 degrees Celsius. The substrate 810 is maintainedat this temperature for a time sufficient to allow the desired amount offilter material to diffuse in the substrate 810. This time period may bein the range of a few minutes to several hours, depending on theparticular filter material, substrate 810 material, and filteringspecifications, until the filter material is sufficiently diffused inthe substrate 810.

In certain embodiments, the filter material, such as pigment material,diffuses only through a portion of the thickness of the substrate 810.For example, the dark tinting 830 may extend only through about 1/N ofthe thickness of the substrate 810, where N is a positive integer.Accordingly, depending on the filtering specifications, the heating anddiffusion process may be modified in order to cause diffusion to adesired depth of the substrate 810.

In other embodiments, the filter material may be incorporated in thesubstrate 810 as the substrate is being formed. For example, in variousembodiments the substrate 810 comprises a polymer material that is madeby melting polymer pellets and forming a sheet of melted polymermaterial. A filter material, such as pigment, may be added to thepolymer pellets prior to heating, or during heating, and mixed with themelted pellets. Thus, the filter material may be substantially uniformlydiffused in the melted polymer and in the resultant polymer substrate810. A similar process may be used to incorporate a filter material in aglass substrate 810.

In one embodiment, because of the relative thickness of the substrate810, the density of the absorber pigments in the dark tinting 830 doesnot need to be as high as when the tinting is in the form of a thinfilm. Filters may alternatively comprise one or more thin films that areadhered to either side of the substrate of an interferometric modulator.When these one or more thin films are added to an interferometricmodulator, a total thickness of the interferometric modulator structureis increased by at least a thickness of the thin films. Theinterferometric modulator embodiments described herein advantageouslyincorporate filter material in the substrate of interferometricmodulators, thus reducing or minimizing the total thickness of theinterferometric modulator structure when compared to a similarinterferometric modulator having similar filter material in a separatethin film.

FIG. 9 is a cross section of an interferometric modulator 900 havingcolored tinting 930 incorporated in a substrate 910. The exemplaryinterferometric modulator 900 comprises a light modulating element 960including a movable mirror 906 separated from a partial reflector 902 bysupports 904. In FIG. 9, the distance between the movable mirror 906 andpartial reflector 902 is configured so that the interferometricmodulator 900 reflects second order red light. In the embodiment of FIG.9, the partial reflector 902 is adjacent the substrate 910 that includescolored tinting 930. Exemplary FIG. 9 also illustrates a dielectric 920in the light modulating element 960 and a viewing eye 510.

As explained above, interferometric modulators are configured so that adistance between two reflective surfaces creates constructiveinterference that results in particular wavelengths of light beingreflected. In one embodiment, the optical path length d betweenreflective surfaces, such as the movable mirror 906 and the partialreflector 902, of approximately ½ the wavelength of a particular colorof light will allow the reflected light of that color to experienceconstructive interference, thus reflecting that color back to a viewer.As is well know in the art, optical path length factors in the index ofrefraction of the medium (e.g., dielectric layer 920) through which thelight propagates.

With respect to FIG. 9, for example, as the optical path length dbetween the partially reflective mirror 902 and movable mirror 906 isincreased, longer wavelengths are, in general, reflected light. Incertain embodiments, constructive interference may also occur when thedistance between the reflective mirror 902 and movable mirror 906 is amultiple of ½ the wavelength of the desired color, such as approximately1× the wavelength and 1½× the wavelength, etc. Each time this occurs,the “order” of the light being generated increases. For example, whenthe gap distance is approximately ½ the desired wavelength, the color iscalled a first order color. When the optical path length d isapproximately equal to the wavelength, it is called a second ordercolor, at approximately 1½×the wavelength is a third order color. In therelaxed state illustrated in FIG. 9, the optical path length d is set toabout the wavelength of red light so that the interferometric modulator900 reflects second order red light.

If a colored pixel is designed to use an interferometric modulator thatreflects a second order red color, the interferometric modulatorspectral characteristics exhibit both a peak in the blue region as wellas the red peak. This is due to the second order red and third orderblue peaks being resonant at the same time. Therefore, the color qualityof the red interferometric modulator may be reduced when compared to afirst order red interferometric modulator. However, the color qualitymay be enhanced by using a red filter to filter out the blue peak. Asshown in FIG. 9, a patterned red tinting 930 is incorporated into thesubstrate 910 over the second order red light modulating element 960.Pigments, dyes, or other filter materials, both known in the art or yetto be devised, may be incorporated into the substrate 910, which maycomprise, e.g., glass or polymer. The systems and methods describedabove with respect to FIG. 8 may be used. For example, a red pigment maybe adhered to the substrate 910, the substrate 910 may be heated, andthe red pigment may diffuse into the substrate 910 so that the substrate910 includes the red pigment material. Other methods and approaches mayalso be used. As noted above, with the patterned tinting 930 in thesubstrate 910, the relative size of the interferometric modulator 900may be smaller than a similar interferometric modulator having a thinfilm red filter.

Those of skill in the art will recognize that a similar technique may beused to filter out any other undesirable spectral peaks appearing atvisual wavelengths in higher order interferometric modulator reflectionsby choosing the appropriate color pigment or dye or color filtermaterial.

FIG. 10 is a cross section of three (first, second, and third) lightmodulating elements 1000A, 1000B, 1000C forming, for example, a pixel ina spatial light modulator array 1001 for a display. The light modulatingelements 1000A, 1000B, 1000C are disposed on a substrate 1010 havingcolored tinting 1030A, 1030B, 1030C aligned with the respective lightmodulating elements. Each of the light modulating elements 1000comprises a movable mirror 1006 separated from a partial reflector 1002by supports 1004. In FIG. 10, the light modulating elements 1000 areconfigured to reflect light in at least three color wavelengths, such asred, green, and blue. In one embodiment, each of the light modulatingelements 1000 exhibit broadband reflectance upon actuation (i.e., almostno gap between the movable mirror 1006 and the partial reflector 1002except for a dielectric material layer in some embodiments). In thisexemplary embodiment, in the actuated state, each light modulatingelement acts as a fully reflective mirror, reflecting every wavelengthof incident light.

In the embodiment of FIG. 10, a wavelength of light viewable by theviewing eye 510 from each light modulating element 1000 is adjusted byincorporating colored filters 1030 in the substrate 1010. For example,the interferometric modulator array 1001 comprises a red tinting 1030Aforward of the first light modulating element 1000A, a blue tinting1030B forward of the second light modulating element 1000B, and a greentinting 1030C forward of the third light modulating element 1000C. Thus,the array 1001 provides three colors from light modulating elementshaving the same dimensions. In this embodiment, manufacturing of colorinterferometric modulator displays may be simplified because an entiredisplay may be made with the same gap distance between the movablemirror 1006 and partial reflector 1002 and patterning the substrate toinclude color filters. In one embodiment, the three light modulatingelements 1000A, 1000B, 100C comprise a pixel of a display.

Any suitable colored pigments known in the art for achieving coloredtinting (e.g., of glass or polymer) may be incorporated into thesubstrate 1010. Other pigments, dyes, or coloring materials may also beused. In one embodiment, the patterned tinting 1030A, 1030B, 1030C isincorporated in the substrate 1010 by forming patterns of pigmentmaterial onto the surface of the substrate 1010 using a mask, forexample. Other techniques, such as those described above with referenceto FIG. 8, may also be used in order to pattern the filter material onthe substrate 1010. In one embodiment, in order to selectively applythree different filter materials, such as a red, green and blue pigment,to the substrate 1010, three patterning steps, such as thephotolithography or ink-jet techniques described above, are sequentiallyperformed. As described above with reference to FIG. 8, the substrate1010 may be heated to allow the pigment material to diffuse into thesubstrate 1010. A wide range of methods of fabricating these arrays 1001and the substrates 1010 are possible.

In certain embodiment, an interferometric modulator may include fewer ormore colors patterned in a substrate than described with reference toFIG. 10. In other embodiments, a substrate including multiple coloredpatterning, such as the substrate 1010, may also include dark tintingforward of the supports and edge portions of the modulating elements. Inthis embodiment, four patterning steps may be performed to apply thethree colors and the dark tinting in the desired locations on thesubstrate. In one embodiment, after the multiple filter materials arepatterned on the substrate 1010, the substrate is heated to a sufficienttemperature for a sufficient time so that each of the filter materialsdiffuse in the substrate 1010.

FIG. 11A is a cross section of another interferometric modulator 1100having colored tinting 1130 in the substrate 1110. The exemplaryinterferometric modulator 1100 comprises a light modulating element 1160comprising a movable mirror 1106 separated from a partial reflector 1102by supports 1104. In FIG. 11A, a distance between the movable mirror1106 and partial reflector 1102 is configured so that the lightmodulating element 1160 reflects first order green light. In theembodiment of FIG. 11A, the partial reflector 1102 is adjacent asubstrate 1110 that includes colored tinting 1130. Exemplary FIG. 11Aalso illustrates a dielectric 1120 in the light modulating element 11630and a viewing eye 510.

As noted above, the light modulating element 1160 is configured toreflect first order green light, which may have a greater perceivedbrightness and contrast to a viewing eye 510 when compared to othercolors of light. However, it may be desirable that the bright pixelsappear white instead of green. Thus, in the embodiment of FIG. 11A, thecolored tinting 1130 comprises a magenta filter that reduces theintensity of wavelengths near the peak of the green spectrum reflectedfrom the light modulating element 1160. With the colored tinting 1130 inthe substrate 1110, light reflected from the interferometric modulator1100 exhibits spectral characteristics that are perceived as white.

In one embodiment, an appropriate magenta colored tinting 1130 isincorporated in the substrate 1110 of an interferometric modulator arraycomprising light modulating elements configured to constructivelymodulate first order green wavelengths. Accordingly, the viewing eye 510perceives the interferometric modulator 1100 as either black or white.As described above, the magenta colored tinting 1130 may be incorporatedby a process of applying an appropriate magenta pigment to the substrate1110 and heating the substrate 1110 in order to allow the pigment todiffuse in the substrate 1110, or through use of other patterningtechniques described herein or known in the art.

FIG. 11B is a graphical diagram illustrating the spectral response ofone embodiment that includes the modulating element 1160 and thesubstrate 1110 incorporating magenta filtering material. The horizontalaxis represents the wavelength of reflected light. The vertical axisrepresents the relative spectral response over the visible spectrum. Atrace 1140 illustrates the response of the light modulating element1160, which is a single peak centered in the green portion of thespectrum, e.g., near the center of the visible spectrum. A trace 1142illustrates the response of the substrate 1110 incorporating magentafiltering material. The trace 1142 has two relatively flat portions oneither side of a central u-shaped minimum. The trace 1142 thusrepresents the response of a magenta filter that selectively transmitssubstantially red and blue light while filtering light in the greenportion of the spectrum. A trace 1144 illustrates the combined spectralresponse of the modulating element 1160 and the substrate 1110. Thetrace 1144 illustrates that the spectral response of the combination isat a lower reflectance level than the modulating element 1160 due to thefiltering of light by the filter material incorporated in the substrate1110. However, the spectral response is relatively uniform across thevisible spectrum so that the filtered, reflected light from theinterferometric modulator 1100 is perceived as white.

In some embodiments, gradient tinting may be incorporated into thesubstrate, such as the substrate 1110, so that as the viewing angleincreases from normal to the substrate 1110, the amount of reflectedlight that is filtered by the tinting increases. Thus, the further fromnormal to the substrate a viewer is from an interferometric modulatordisplay, the more dim the image. For example, if the viewing eye 510 ispositioned so that the it sees light reflected from the interferometricmodulator 1100 in direction 1150, which is normal to the front surfaceof the substrate 1110, the viewing eye 510 sees light that has twicepassed through a thickness, t, of the substrate 1110 including thefilter material (e.g., the light passes through the substrate 1110 whenentering the interferometric modulator 1100 and passes through thesubstrate 1110 again when leaving the interferometric modulator 1100).When the viewing eye 510 moves to a position so that it sees lightreflected from the interferometric modulator 1100 in an off-normaldirection 1152, a thickness of the substrate 1110 that the reflectedlight passes through has increased. For example, if the angle betweendirections 1150 and 1152 is about 45 degrees, the thickness of thesubstrate 1110 across direction 1152 is about t*1.414. Accordingly, thelight seen by the viewing eye 150 at direction 1152 has passed throughabout three times the amount of substrate 1110 as the light passesthrough in direction 1150 (e.g., the light passes through a thickness ofabout t*1.4 twice, which is about 2.8t), and through about three timesas much of the filtering material in the substrate 1110. Thus, if thefilter material in the substrate 1110 absorbs certain wavelengths oflight, as the angle between the direction 1150 and the viewing eye 510increases, the amount of the certain wavelengths that are absorbed bythe substrate 1110 will also increase.

FIG. 12A is a cross section of an interferometric modulator 1200 havingfield-of-view filters 1230 incorporated in the substrate 1210. Theexemplary interferometric modulator 1200 comprises a light modulatingelement 1260 including a movable mirror 1206 separated from a partialreflector 1202 by supports 1204. Exemplary FIG. 12A also illustrates adielectric 1220 in the light modulating element 1260 and a viewing eye510.

In some cases, it may be desirable that an interferometric modulatordisplay have a limited viewing angle. For example, when using aninterferometric modulator display in an ATM, it may be desirable thatthe display is only visible from angles near to perpendicular to thesurface of the display to preserve the privacy of the information beingdisplayed. Furthermore, the color of light reflected from aninterferometric modulator changes with the angle of reflected of light.Accordingly, it may be desirable to remove the viewer observation ofthis color shifting by limiting the viewing angle. In the embodimentdepicted in FIG. 12A, a viewing angle of the interferometric modulator1200 is limited by incorporating field-of-view filters 1230 (alsoreferred to herein as blinds 1230 or baffles 1230) into the substrate1210. By incorporating the blinds 1230 into the substrate 1210 insteadof in a separate film, a substrate 1210 having baffles 1230 separated bya predetermined distance may provide greater angle reduction than a thinfilm having baffles separated by the same predetermined distance, due tothe increased length of the baffles 1230 in the substrate.

As illustrated in FIG. 12A, the blinds 1230 comprise thin structuresthat are substantially perpendicular to the substrate 1210 surface.Thus, light reflected from the light modulating element 1260 that isdirected substantially parallel to the blind structures 1230, such as inan exemplary direction 1250, will pass through the substrate 1210largely unaffected by the blinds 1230. In contrast, light reflected fromthe light modulating element 1260 at other angles, such as in anexemplary direction 1240, may be partially blocked by the blinds 1230,depending on the angle of reflection. Those of skill in the art willrecognize that the field-of-view may be adjusted by selecting the shape,orientation, size, and spacing of the blinds 1230. For example, thebaffles 1230 may have a size, shape, and spacing to provide afield-of-view no more than about ±20 degrees as measured about thedirection 1250, which is normal to a front surface 1211 of the substrate1210. The field-of-view may therefore be between about ±20, ±25, ±30,±35 and ±40 degrees or less as measured about the direction 1250. In oneexemplary embodiment, the baffles 1230 provide the display 1200 with afield-of-view of about ±30 degrees normal to the front surface 1270.

A variety of techniques may be used to create the baffles 1230. In oneembodiment, glass laminates are used. In this embodiment, one or moreglass laminates may be patterned with filter materials and heatedtogether to form a single substrate incorporating the filter material.In another embodiment, a first laminate may be patterned with a filtermaterial, using one or more of the techniques described above, forexample, and a second laminate may be placed on the patterned surface ofthe first laminate. The laminates may then be heated in order toconcurrently diffuse the filter material into both of the laminates. Inthis embodiment, the filter material may advantageously be located inthe centered of the formed substrate structure. In addition, because thefilter material concurrently diffuses into two materials, the heatingtime may be reduced.

In other embodiments, filter materials are formed into thin lines ontothe surface of the substrate using one or more techniques describedabove. In one embodiment, the substrate is patterned with a grid patternusing one or more of the techniques described above. In embodimentswhere the filter material is diffused in the substrate in order to formbaffles, the heating time may be reduced so that lateral diffusion intothe substrate is reduced or minimized, while allowing the filtermaterial to diffuse into a top surface of the substrate. In oneembodiment, the filter material is diffused into only about a top ⅓ ofthe substrate when forming baffles.

Because the baffles are intended to substantially absorb light reflectedfrom certain angles of the modulating element 1260, in certainembodiments the baffles are as thin as possible. In addition, in certainembodiments the filter material used to form the baffles 1230 comprisesa material that diffuses in the heated substrate in a substantiallynormal direction to a surface of the substrate 1210. In anotherembodiment, the filter material used to form baffles has a highermelting point than the substrate 1210 so that when the substrate 1210 isheated, the filter material sinks into the substrate material, withoutsignificant diffusion. Thus, the baffles 1230 are substantially thethickness of the higher melting point filter material. In oneembodiment, a ceramic material may be used for such a filter material.In one embodiment, a ceramic material may be patterned in a series ofrows, columns, or a grid configuration, and then a molten substratematerial may be poured over the patterned ceramic material. When thesubstrate material hardens, the patterned ceramic material will formbaffles in the substrate.

FIG. 12B is a perspective side view and FIG. 12C is a top view of anexemplary substrate 1211 having baffles 1261 incorporated in thesubstrate 1211. In the embodiment of FIGS. 12B and 12C, the baffles 1261are substantially vertically aligned columnar features. In oneembodiment, the outer surfaces 1262 a of the baffles 1261 are coatedwith an opaque material. The baffles 1261 may be disposed in thesubstrate 1211 by any of the methods discussed above, such as by heatingthe substrate 1211, placing the baffles on a top surface of thesubstrate 1211, and allowing the baffles to sink into the substrate1211.

In certain embodiments, the baffle structures 1230, 1261 shown in FIGS.12A-12C may comprise reflective material. If a portion of the baffle1230, 1261 nearest to the light modulating element is substantiallyreflective, then light reflected from the light modulating element thatis incident on the reflective portion of the baffle 1230, 1261 will notpass through the substrate 1210, 1211, but will be reflected back to thelight modulating element. In certain embodiments, the outer surfaces1263 of the baffle structures 1261 (FIG. 12B) may be made of asubstantially reflective material, such as a flash coating ofsubstantially reflective material.

FIG. 13 is a cross section of an interferometric modulator 1300 havingphotoluminescent materials 1330 in the substrate 1310. The exemplaryinterferometric modulator 1300 comprises a light modulating element 1360including a movable mirror 1306 separated from a partial reflector 1302by supports 1304. In the embodiment of FIG. 13, the partial reflector1302 is adjacent a substrate 1310 that includes photoluminescentmaterial 1130. Exemplary FIG. 13 also illustrates a dielectric 1320 inthe light modulating element 1360 and a viewing eye 510.Photoluminescent materials, as used herein, includes those materialsthat have phosphorescent and/or fluorescent properties. Examples ofpossible photoluminescent materials include those described in U.S. Pat.No. 6,278,135 to LUMI (long afterglow photoluminescent pigment, fromGlobal Trade Alliance Inc, Scottsdale, Ariz.), and the materials thatcomprise BC-482A and BC-484, wavelength shifter bars (Saint-GobalnCrystals and Detectors, Newbury Ohio).

In various embodiments, the photoluminescent material 1330 providesfront illumination of the interferometric modulator 1300 upon excitationwith appropriate light. For example, in certain embodiments a lightsource 1344 comprises a short wavelength light source, such as a blueLED, that may be used to excite the photoluminescent material 1330,which then emits light 1340 at longer wavelengths. In one embodiment,multiple photoluminescent materials 1330 are incorporated to emit lightat different wavelengths in light modulating elements. For example, oneset of interferometric modulators may include a photoluminescentmaterial 1330 that emits light having spectral characteristics similarto light reflected by blue modulating elements, another set ofinterferometric modulators may include a photoluminescent material 1330that emits light having spectral characteristics similar to lightreflected by green modulating elements, and a third set ofinterferometric modulators may include a photoluminescent material 1330that emits light having spectral characteristics similar to lightreflected by red modulating elements. Thus, by altering thephotoluminescent material 1330 associated with light modulating elementsin an array, a monochrome display may be converted to a multi-colordisplay.

In one embodiment, the excitation light source 1344 may be located suchthat the light 1342 contacts the substrate 1310 from the side of theinterferometric modulator 1300. In this embodiment, the photoluminescentmaterial 1330 advantageously emits light 1340 in all directions, thusproviding substantially uniform illumination within the light modulatingelement 1360.

In other embodiments, the light source 1344 may be located at any otherlocation proximate the substrate 1310 of the interferometric modulator1300. The photoluminescent materials 1330 may be incorporated into thesubstrate 1310 as small particles or may be dissolved into the substrate1310, such as by the heating and diffusing methods described above withreference to other embodiments. Alternatively, the photoluminescentmaterials 1330 may be uniformly mixed into the substrate 1310 as thesubstrate 1310 is formed. Other methods may be used as well. Those ofskill in the art will recognize many photoluminescent materials thatwill be suitable for front lighting of an interferometric modulatordisplay. Photoluminescent material both well known, as well as those yetto be devised, may be employed.

A wide range of variation in design and configuration are also possible.In addition to incorporating different materials into the substrate, indifferent quantities, for different applications, a variety of differentpatterning may be used. The amount or type of material introduced intothe substrate may vary with depth in the substrate or may varylaterally, for example, to create gradation and to form differentpatterns. The size of the features in the pattern may also vary.Combination of materials may be introduced into the substrate. Stillother variations in the configuration and resultant structures as wellas methods of fabrication are possible.

Moreover, the foregoing description details certain embodiments of theinvention. It will be appreciated, however, that no matter how detailedthe foregoing appears in text, the invention can be practiced in manyways. As is also stated above, it should be noted that the use ofparticular terminology when describing certain features or aspects ofthe invention should not be taken to imply that the terminology is beingre-defined herein to be restricted to including any specificcharacteristics of the features or aspects of the invention with whichthat terminology is associated. The scope of the invention shouldtherefore be construed in accordance with the appended claims and anyequivalents thereof.

1. A method of forming a display device, the method comprising:diffusing a material into a substrate, said material having a differentoptical property than said substrate; and forming at least one lightmodulating element over the substrate, the light modulating elementcomprising a partially reflective surface and a substantially reflectivesurface that form an optical cavity, at least one of said reflectivesurfaces movable with respect to the other to modulate said opticalcavity.
 2. The method of claim 1, further comprising depositing thematerial over the substrate.
 3. The method of claim 2, furthercomprising heating the substrate.
 4. The method of claim 2, furthercomprising heating the substrate to a temperature in the range of about200 to 250 degrees Celsius.
 5. The method of claim 3, wherein thesubstrate is heated for a time sufficient to diffuse the material to apredetermined level within the substrate.
 6. The method of claim 5,wherein the predetermined level is less than about ⅓ of a thickness ofthe substrate.
 7. The method of claim 5, wherein the predetermined levelis greater than about ⅓ of a thickness of the substrate.
 8. The methodof claim 1, wherein at least one optical characteristic of the materialchanges as the material diffuses into the substrate.
 9. The method ofclaim 1, further comprising applying the material to the substrate. 10.The method of claim 9, wherein applying comprises spraying the material.11. The method of claim 9, further comprising positioning a mask on thesubstrate prior to applying the material to the substrate.
 12. Themethod of claim 1, wherein the substrate comprises at least one of:glass and polymer.
 13. The method of claim 1, wherein the materialcomprises black pigment.
 14. The method of claim 1, wherein the materialcomprises colored pigment.
 15. The method of claim 1, further comprisingdiffusing different materials into the substrate.
 16. The method ofclaim 15, wherein different materials are diffused for different lightmodulating elements.
 17. A display device formed by the process ofclaim
 1. 18. A display device comprising: at least one light modulatingelement comprising first and second reflective surfaces, said secondsurface being movable with respect to said first surface; and asubstrate, said light modulating element disposed over said substrate,wherein said substrate comprises a color filter that transmits colorlight.
 19. The display device of claim 18, wherein the substratecomprises a plurality of color filters that transmit different colorlight when illuminated by white light.
 20. The display device of claim19, wherein the color filters have different colors for different ofsaid light modulating elements.
 21. The display of claim 19 wherein saidplurality of color filters include red, green, and blue color filtersthat transmits red, green, or blue light, respectively, when illuminatedby white light.
 22. The display device of claim 18, wherein said colorfilter comprises a magenta color filter that transmits magenta lightwhen illuminated with white light.
 23. The display device of claim 18,wherein said color filter comprises pigment.
 24. The display device ofclaim 18, wherein the color filter is substantially opticallytransmissive to visible light in a first wavelength region andsubstantially absorptive to visible light in a second wavelength region.25. The display device of claim 24, wherein the first wavelength regionincludes red wavelengths and said second wavelength regions includesother wavelengths such that said color filter is substantially opticallytransmissive to red light when illuminated with white light.
 26. Thedisplay device of claim 24, wherein the first wavelength region includesgreen wavelengths and said second wavelength regions includes otherwavelengths such that said color filter is substantially opticallytransmissive to green light when illuminated with white light.
 27. Thedisplay device of claim 24, wherein the first wavelength region includesblue wavelengths and said second wavelength regions includes otherwavelengths such that said color filter is substantially opticallytransmissive to blue light when illuminated with white light.
 28. Thedisplay device of claim 24, wherein the light modulating element isconfigured to reflect light in said first wavelength region.
 29. Thedisplay device of claim 18, wherein the light modulating element isconfigured to reflect second order red and third order blue and thecolor filter is substantially optically transmissive to second order redand absorbs third order blue.
 30. The display device of claim 18,wherein the light modulating element is configured to substantiallyreflect green light and the color filter is substantially opticallytransmissive to magenta light when illuminated with visible light. 31.The display device of claim 18, wherein the color filter comprises oneor more pigments.
 32. The display device of claim 18, wherein the colorfilter comprises one or more photoluminescent materials.
 33. The displaydevice of claim 18, wherein as an angle between a direction of lightreflected normal to a surface of the substrate increases, filteringperformed by the color filter increases.
 34. The display device of claim18, further comprising one or more supports for supporting one of saidreflective surfaces.
 35. The display device of claim 18, wherein thecolor filter is patterned on the substrate so that the color filter issubstantially forward of the one or more supports.
 36. The displaydevice of claim 18, further comprising: a processor that is inelectrical communication with said at least one light modulatingelement, said processor being configured to process image data; and amemory device in electrical communication with said processor.
 37. Thedisplay device of claim 36, further comprising: a driver circuitconfigured to send at least one signal to at least one light modulatingelement.
 38. The display device of claim 37, further comprising: acontroller configured to send at least a portion of said image data tosaid driver circuit.
 39. The display device of claim 36, furthercomprising: an image source module configured to send said image data tosaid processor.
 40. The display device of claim 39, wherein said imagesource module comprises at least one of a receiver, transceiver, andtransmitter.
 41. The display device of claim 36, further comprising: aninput device configured to receive input data and to communicate saidinput data to said processor.
 42. A display device comprising: at leastone light-modulating element comprising first and second reflectivesurfaces, said second surface being movable with respect to said firstsurface; and a substrate, said light-modulating element disposed oversaid substrate, wherein said substrate incorporates at least tinting.43. The display device of claim 42, wherein said tinting is configuredto absorb substantially all wavelengths of visible light and the tintingis disposed forward of a support for said first reflective surface. 44.The display device of claim 43, wherein said support comprises a poststructure.
 45. A display device comprising: a plurality oflight-modulating elements each comprising first and second reflectivesurfaces, said second surface being movable with respect to said firstsurface; and a substrate, said plurality of light-modulating elementsdisposed over said substrate, wherein said substrate includes thereinfirst and second absorptive regions, said first and second absorptiveregions having different optical transmission properties.
 46. Thedisplay device of claim 45, wherein said first regions comprise colorfilters that transmit a color when illuminated by white light.
 47. Thedisplay device of claim 45, wherein said first regions are below saidlight modulating elements and said second regions are below areasbetween said light-modulating elements.
 48. The display device of claim45, wherein said first regions comprise color filters having differentcolors for different of said light modulating elements.
 49. The displaydevice of claim 45, wherein said first regions comprise masks.
 50. Thedisplay device of claim 45, wherein said first regions are belowsupports for said first reflective surfaces and said second regions arebelow areas between said supports.
 51. The display device of claim 45,wherein said first regions comprise material diffused into saidsubstrate.
 52. The display device of claim 51, wherein said secondregions are substantially devoid of said material diffused in said firstregions.
 53. The display device of claim 45, wherein said first regionscomprise pigmented regions.
 54. A display device comprising: at leastone plurality of light modulating elements each comprising first andsecond reflective surfaces, said second surfaces being movable withrespect to said first surfaces; and a substrate, said at least oneplurality of light modulating elements disposed over said substrate,wherein said substrate comprises a plurality of elements configured tolimit a field-of-view of the display device.
 55. The display of claim54, wherein the plurality of elements configured to limit afield-of-view of the display comprises a plurality of baffles.
 56. Thedisplay of claim 55, wherein the substrate is in a horizontal plane andthe plurality of baffles comprise substantially planar surfacessubstantially parallel to a vertical plane.
 57. The display of claim 55,wherein the plurality of baffles comprise spacings between individualbaffles, said spacing having a dimension that provides a view angle ofnot more than about 40 degrees from a plane normal to said substrate,wherein the angle is measured as a half-angle with respect to the normalplane.
 58. The display of claim 55, wherein the plurality of bafflescomprise spacings between individual baffles, said spacing having adimension that provides a view angle of not more than about 20 degreesfrom a plane normal to the substrate, wherein the angle is measured as ahalf-angle with respect to the normal plane.
 59. The display of claim55, wherein the plurality of baffles are substantially opaque.
 60. Thedisplay of claim 59, wherein the plurality of baffles comprisesubstantially planar opaque surfaces.
 61. The display of claim 55,wherein the plurality of baffles comprises absorbing material.
 62. Thedisplay of claim 55, wherein the plurality of baffles comprises areflecting material.
 63. A method of forming an interferometricmodulator, the method comprising: combining a substrate material with afilter material in order to form a mixture; heating the mixture so thatthe substrate material substantially melts and the filter material isdiffused within the melted substrate material; cooling the mixture inorder to form a substrate; and forming at least one light modulatingelement over the substrate, the light modulating element comprising apartially reflective surface and a substantially reflective surface thatform an optical cavity, at least one of said reflective surfaces movablewith respect to the other to modulate said optical cavity.
 64. Themethod of claim 63, wherein the raw substrate material comprises atleast one of: polymer pellets, sand, flint, or quartz.
 65. The method ofclaim 63, wherein the substrate material is at least partially moltenwhen combined with the filter material.
 66. The method of claim 63,wherein the substrate material is not molten when combined with thefilter material.
 67. A display device comprising: means for modulatinglight; and means for supporting said light modulating means; and meansfor filtering light disposed in said supporting means.
 68. The apparatusof claim 67, wherein said modulating means comprises first and secondreflective surfaces, said second reflective surfaces being movable withrespect to said first reflective surface.
 69. The apparatus of claim 68,wherein said supporting means comprises a substrate.
 70. The apparatusof claim 69, wherein said filtering means comprises a color filter,photoluminescent material, or a mask.
 71. A display device comprising:means for modulating light; and means for supporting said lightmodulating means; and means for limiting a field-of-view.
 72. Theapparatus of claim 71, wherein said modulating means comprises first andsecond reflective surfaces, said second reflective surfaces beingmovable with respect to said first reflective surface.
 73. The apparatusof claim 72, wherein said supporting means comprises a substrate. 74.The apparatus of claim 73, wherein said field-of-view limiting meanscomprises baffles.
 75. A display device comprising: at least onelight-modulating element comprising first and second reflectivesurfaces, said second surface being movable with respect to said firstsurface; and a substrate, said light-modulating element disposed oversaid substrate, wherein said substrate incorporates at least onephotoluminescent material.
 76. The display device of claim 75, whereinthe at least one photoluminescent material comprises at least one of:phosphorescent and fluorescent materials.
 77. The display device ofclaim 75, wherein the at least one photoluminescent material illuminatesthe light modulating element when excited by a light source.
 78. Thedisplay device of claim 75, wherein illumination from thephotoluminescent material comprises light having a wavelength largerthan a wavelength of the light source.